The invention relates to a cathode ray tube having an envelope, comprising on the one side a luminescing screen and on the other side a neck portion, having an electron gun which is positioned in the neck portion and which includes a beam-forming portion and a focusing structure, the focusing structure including an open-ended hollow tube of an electrically insulating material, having an inner surface on which a layer of a material having a high electrical resistance is deposited and a getter arrangement provided in the envelope.
Such a cathode ray tube can be used in black/white colour and projection television, in arrangements for displaying figures and letters (Data Graphics Display) and in other arrangements in which a cathode ray tube is used.
Although in theory an accurate focusing may be obtained by means of a layer of a material having a high electrical resistance, which layer is, for example, of a helical structure and over whose extremity a voltage difference is applied, it was found in practice that the focusing does not always come up to the expectations.